The present invention relates to hydraulic circuits for supplying hydraulic fluid to slide portions and valve controllers of internal combustion engines.
One of the hydraulic circuits is disclosed, for example, in JP-A 4-175431. This hydraulic circuit includes first and second hydraulic pumps arranged independently. The first pump sucks hydraulic fluid within an oil pan to discharge it to a first discharge passage that communicates with a main gallery, whereas the second hydraulic pump sucks hydraulic fluid within the discharge passage to discharge it to a second discharge passage that communicates with a valve controller.
Connected to each discharge passage is a relief passage communicating with the oil pan and having a relief valve for opening the relief passage at a predetermined pressure. The relief valve serves to maintain the pressure within the corresponding discharge passage at a predetermined value.
Specifically, connected to the first discharge passage is the first relief passage communicating with the oil pan and having the first relief valve for opening the first relief passage at a predetermined pressure for the first discharge passage. The first relief valve carries out relief action to maintain the pressure within the first discharge passage at a predetermined value. Connected to the second discharge passage is the second relief passage communicating with the oil pan and having the second relief valve for opening the second relief passage at a predetermined pressure for the second discharge passage. The second relief valve carries out relief action to maintain the pressure within the second discharge passage at a predetermined value.
Hydraulic fluid discharged to the first discharge passage is supplied, through the main gallery, to the slide portions for lubrication thereof. On the other hand, hydraulic fluid discharged to the second discharge passage is supplied to the valve controller for operation thereof.
With the known hydraulic circuit, however, in view of the fact that the first relief passage connected to the first discharge passage communicates with the oil pan, and the second relief passage connected to the second discharge passage also communicates with the oil pan, the first hydraulic pump needs a discharge capacity Q1 required to lubricate the slide portions, and the second hydraulic pump needs a discharge capacity Q2 required to operate the valve controller.
The valve controller is operated under a predetermined operating condition of the internal combustion engine, and is not operated in the normal operating condition thereof. And the pressure within the second discharge passage is maintained at a predetermined value by relief action of the second relief valve. Specifically, the second hydraulic pump always discharges the quantity Q2 of hydraulic fluid required to operate the valve controller, while when the valve controller is not operated, the second relief valve is opened to ensure hydraulic circulation to the oil pan.
Therefore, when the valve controller is not operated, the second hydraulic pump carries out needless work of circulating hydraulic fluid within the second discharge passage to the oil pan, resulting in a waste of power.
It is, therefore, an object of the present invention to provide hydraulic circuits for internal combustion engines, which include hydraulic pumps with saved power and reduced size.
One aspect of the present invention lies in providing a hydraulic circuit, comprising:
first and second pumps;
a first discharge passage receiving hydraulic fluid discharged from said first pump, said first discharge passage communicating with a main gallery; a second discharge passage receiving hydraulic fluid discharged from said second pump, said second discharge passage communicating with an actuator;
a communication passage ensuring communication between said first and second discharge passages; and
a relief valve arranged with said communication passage, said relief valve being opened at a predetermined pressure for said second discharge passage.
Another aspect of the present invention lies in providing a hydraulic circuit, comprising:
a pump with first and second ports;
a first discharge passage receiving hydraulic fluid discharged through said first port of said pump, said first discharge passage communicating with a main gallery;
a second discharge passage receiving hydraulic fluid discharged from said second port, said second discharge passage communicating with an actuator;
a communication passage ensuring communication between said first and second discharge passages; and
a relief valve arranged with said communication passage, said relief valve being opened at a predetermined pressure for said second discharge passage.